This study is an interdisciplinary investigation focusing on two major topics: (a) the individual phonological knowledge of a large group of speech disordered children and (b) the individual learning patterns as they occur either spontaneously or as a result of clinical intervention. Research techniques and findings from linguistic theory and speech pathology are combined to address these two topics, each of which is independently of interest to either discipline. Descriptions of phonological knowledge and of learning patterns for this popoulation are extremely limited; even less is known about the possible relationship between the two. The proposed study will permit an in-depth investigation of the relationship between phonological knowledge and learning by gathering extensive and comprehensive data on both. Phonological knowledge is assessed through conventional techniques of linguistic analysis and include statements about the phonetic and phonemic inventories, the mental representation of lexical items, and the phonological rules governing speech production. Learning patterns are shown by an increase in correct speech productions measured during either a three month baseline period or a three month clinical treatment period. Specifically, the objectives of this research on phonologically disordered children are: (1) to provide comprehensive individualized phonological descriptions and typological characterizations of 40 subjects, (2) to provide descriptions and typological characterizations of a variety of individual learning patterns for the same subjects, (3) to formulate and test several hypotheses that predict learning patterns based on phonological knowledge, and (4) to provide a further description of phonological knowledge at a point in time following treatment to determine possible changes in phonological knowledge. The findings from this study will have both theoretical and applied significance. The use of an interdisciplinary approach to these problems is essential and offers an opportunity for gaining new insights on basic issues in both phonological theory and speech pathology.